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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Support for Exotic Superconductivity Theory
10 April 1998 7:00 pm
A radical theory of high-temperature superconductivity--electric conduction with no resistance at comparatively high temperatures--has won its first experimental support. In today's Science, researchers describe how these superconductors are completely different from conventional low-temperature superconductors. Experts say the findings are the first convincing evidence that superconductive compounds work according to two entirely different mechanisms.
There's no mystery to low-temperature superconductors. When a superconducting material is cooled to a few degrees above absolute zero, some of its electrons hang out in pairs and "condense" into a single quantum state--similar to how steam condenses to water when cooled. Arranged like that, electrons are difficult to scatter and can move with no resistance. A few years ago, some physicists suggested that high-temperature superconductors--which operate at about -200 degrees Celsius--worked backwards: most of the electrons pair, but only a few condense. An ingenious explanation for this odd behavior was provided by the controversial charge-stripe theory, which holds that charge and spin can be separated on the electron.
Zhi-Xun Shen of Stanford University and his colleagues wanted to test some of the predictions of the new theory. They bombarded a high-temperature superconductor called bismuth-strontium-calcium-copper oxide with photons. By measuring the energy and momentum of electrons knocked out of their orbits by the photons, the researchers were able to confirm that all electrons were paired. Unlike in low-temperature superconductors, the pairings were somehow taking place between electrons of completely different momenta. Moreover, the typical momentum transfer between the electrons and the material was exactly that predicted by charge-stripe theory.
If that momentum had been missing, stripe theory would be dead, says Steven Kivelson, a physicist at the University of California, Los Angeles, and an originator of the theory. The experiment isn't the last word on stripe theory, he says, but the evidence of paired electrons proves that standard theory fails to explain high-temperature superconductivity.